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Asphalt Barge Poses Concerns for Cables

8/2/2000

DC Maritime Technologies Inc. (Vancouver, Canada) have recently been awarded a contract to prepare the electrical design for an asphalt-carrying barge. Though simple from an electrical perspective the barge has a relatively large power demand requiring 2—350 kW generators. The asphalt is heated using oil-fired boilers. The major electrical installation problem to overcome has been the elevated temperature across the deck caused by the heated asphalt.

Then high temperatures affect the cable installation, floodlights, winches and anchor windlass etc. The deck of the barge is likely to operate at around 160 deg. C. with maximum temperatures around 180 deg. C. To provide a modicum of protection, the cables are to be installed inside an insulated cable duct running across the deck. Ventilation fans will be installed to keep the duct temperature at the design ambient for the cables.When subjected to high temperatures, both the cable insulation and conductor must be reviewed to determine:

The effects on the cable insulation if a ventilation failure occurred.

The minimum cable insulation requirements for the application.

The applicable conductor ampacity de-rating needed for high temperature operation.

Of interest is the insulation deformation. If glass, ceramic or similar insulations were used, deformation would be insignificant but costs extremely high. Thermoplastic insulations (e.g. PVC) deform easily but their costs are minimal. A compromise is thermosetting type insulation (EPR), which has moderate operating temperature levels at reasonable cost. The EPR insulations can withstand high ambient temperatures without short-term damage. It is significant to note however that the cable lifespan is reduced from 22 years (operating at 90 deg C) to two weeks if operated at 160 deg C.

Based on the above the design was progressed using standard cable types, recognizing that a short-term ventilation failure would not require the cables to be immediately replaced. By careful conductor sizing (reduced cable ampacity), certain services can remain in operation until ventilation failures were rectified.